Microlithography is used for producing microstructured components such as integrated circuits or LCDs, for example. The microlithography process is carried out in a so-called projection exposure apparatus having an illumination device and a projection objective. In this case, the image of a mask (reticle) illuminated via the illumination device is projected, via the projection objective, onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection objective, in order to transfer the mask structure to the light-sensitive coating of the substrate.
It is known that, in the microlithography process, the imaging contrast can be significantly improved if the mask is illuminated with linearly polarized light, wherein the preferred direction of this polarization is expediently parallel to the longitudinal direction of the grating structures present on the mask. In this case, an as far as possible constant polarization distribution in the entire reticle field is also desirable for a constant imaging contrast and hence a defect-free imaging of the grating structures.
In this case, however, the problem can occur that a polarization distribution originally present (generally linear polarization upon entry into the illumination system) can be altered to different extents by polarization-influencing effects (e.g. stress birefringence induced by mount components in the material of the optical components such as, for example, lenses, polarization-influencing effects of dielectric layers, etc.).
US 2007/0146676 A1 discloses, among other things, arranging in a pupil plane of the illumination device, or in the vicinity thereof, a polarization manipulator for converting the polarization state, which has a plurality of variable optical rotator elements that can be used to rotate the polarization direction of impinging, linearly polarized light with a variably adjustable rotation angle. The variable rotation angle or polarization state provided by the rotator elements can be set in accordance with the measurement result supplied by a device for measuring the polarization state.